Delayed pulse generator



:saw'tooth and .the vinstant of anode conduction.

United .States Patent DELAYED PULSE GENERATOR z:Joseph P. Gleason, Encino, Calif., assigner to the United "States'of vAmerica as represented-by'the Secretary of the-Air-Force Application September 15, 1955,:Serial No. 534,631

4Claims. (Cl. Z50-27) This invention relates to4 delayed pulsevgenerato'rs par- The type of .delayed pulse generator to which this invention relates comprises a triode-vacuum tube-having a ysawtooth of voltage applied to the control grid and la 7positive control potential applied to the cathode. The

ltube is normally cut oi at the startof the/sawtooth grid fvoltage vbut,.as they grid voltage rises linearly, -anode'con- =.ductionfeventually starts at a grid voltage"determined'by .the value of the control potential. Therefore, -by 'con- -ftrolling the value of the control potential acont-rol Vcan ybe exerted. over the time. interval 'betweenthe start of. the The Ianode Voltage may Ibe differentiated to produce anega- :tive pulse at this instant.

A delay circuit of the abovetype suffers from the drawback that, before conduction, the anode voltage of the tube is a'function of the control potential. This means that the tube characteristics arev afunction of the control potential. The most 'important characteristics z of the tube in this case` is its cut-olf grid voltage. fIf' this fparticular characteristic is not a linear function offthe control potential then the delay produced by the circuit will likewise not be a linear function of the control potential.

It is the principal object of this invention to overcome the above diiculty. Briefly, this is accomplished by connecting a gas-lled Voltage regulating tube between the cathode of the triode and a point on its anode load resistor. The potential of this point is therefore substantially xed relative to the cathode with the result that the anode-cathode voltage during cut-off is made independent of the control potential. An added advantage is also obtained from the relatively lower anode potential resulting from the use of the voltage regulating tube. Mechanical movement of the control grid due to mechanical shock or temperature changes may change the cut-olf point. This ecect is reduced by the lowered tube operating voltage.

A more detailed description of the invention will be given in connection with the speciiic embodiment thereof shown in the accompanying drawings in which,

Fig. l `shows in block form an automatic range tracking circuit utilizing the invention,

Fig. 2 illustrates the operation of Fig. l, and

Fig. 3 is a schematic diagram of a delayed pulse generator in accordance with the invention.

Fig. l illustrates the use of the delayed pulse generator in an automatic range tracking circuit as found in certain :radar systems. Synchronizing or trigger pulses, which are coincident with the radiated radar pulses, are applied to sawtooth generator i which operates in response to each trigger pulse to generate one sawtooth Wave varying .the termination of the sawtoothy and return of the tube gate pulse width, to late gated video ampliiier9. The video vsignal representing all'targets in the iield of view vof the rada-r apparatus Ais applied to the inputs of v'both `video amplifiers over circuitli).

- from the vtotal video signal the signal-representing*the 'ice linearly with time and starting 'coincidently with :the applied pulse. The sawtooth voltages are applied ftof'the grid of delay triode 2 which also has a control potential :applied over circuit 3 toits cathode. Ihe tube's in cutot'at thestartof each applied sawtooth and the amplitudeof the control potential determines the instantaneous value of the sawtooth voltage, and hence the time after Ythe 'trigger pulse, at which anode conduction occurs. The

parameters'are such that the tube saturates soona'fter conduction'starts s'o that av substantially square *wave-"of voltage appears on the anode. Differentiation of the leading edges of this square wave lby'cir'cuit 4 produces sharp negative pulses coincident with the initiations of anode conduction in the tube. The trailing'edges 'of the square waver produce' positive pulses-which coincide with to the nonconductive state.

The -delayed negative pulses in the youtput of differentiating circuit 4 are 'applied to 'rang'egate blocking-oscillatorS which is triggered by each negative pulse -to 'produce range' gates 6 of `duration'sr'ibstantially equ'al'to'the duration-of a video echo signal Vfrom .a single target in the'eld of View of 'the vradar apparatus. The range gates are applied without delay toearlyfgated video amplilierf and, aftera delay in circuit tiapproxirnately equal to-the The purpose of v'the'range gate in general isfto isolate target to be tracked. Thepurpose 'of-the early :arid late range gates is to sense the directionY of a change in range. If the target'pulse is centered relative toy'fthe range gates, i. e., if one half of the pulse Lis bracketed by theearly gate and one half by the late-gate, lthe outputs of the twovideo amplifiers aref of equal duration as illustrated under Stationary target in Fig. 2. The outputs y `of these amplifiers are 'applied to tracking 'diodes -1'1 and lllwhich-are lassociated with condenser 13. v'The circuit arrangement is'such that the output 4of early gated video L'amplifier 7 vcauses condenser "13 to dischargethrough tracking diode 11 while the output of late gated video amplier 9 causes condenser 13 to charge through tracking diode 12. Consequently, with equal video output-s, the charging and discharging times are equal and there is no change in condenser voltage. If, on the other hand, the range of the target decreases, the duration of the amplier output increases in the case of the early gated video amplifier 7 and decreases in the case of the late gated video amplier 9, as shown under Decreasing range in Fig. 2. This results in a longer period of discharge than of charge and the condenser voltage therefore decreases. In a similar manner, as illustrated under In creasing range in Fig. 2, an increase in range results in reduced discharging time and increased charging time, which causes the condenser voltage to rise.

The voltage of condenser 13, which is proportional to range, is fed through cathode follower stage 14 and over circuit 3 to delay diode 2 where it becomes the aforementioned control potential. The elect of this potential is to increase or decrease the delay of the early and late range gates as required to keep these gates in position to equally bracket the video target pulse. Thus, an increase in range will operate, by the process described above, to increase the control potential on triode 2 and increase the delay of the range gates so as to restore the original equally bracketed relation of target pulse and range gates. Similarly, a decrease in range will cause the range gates to occur earlier to maintain this relationship.

A schematic diagram of the improved delayed pulse generator is shown in Fig. 3. The triode 2 has a sawf- 2,763,778 p n tooth voltage from generator 1 applied to its grid and the control potential, which in the example of Fig. 1 is the range voltage, applied between cathode and ground. The circuit is initially adjusted so that, with minimum control potential (zero range) on the cathode of tube`2, anode conduction occurs when the sawtooth voltage on the grid just begins to rise. As the control potential is increased, ,higher values of grid voltage are required -to start conduction and correspondingly greater intervals of time occur between the initiation of the sawtooth and anode conduction. The parameters, including the slope `of the sawtooth, are so chosen that conduction, once started, increases rapidly to saturation so that a square wave of reasonably steep wavefront appears on the anode. Differentiation of these wavefronts by circuit 4 produces the negative pulse for triggering the yrange gate blocking oscillator.

Neglecting for the moment the voltage regulator tubje 15, the diIicul-ty with the above described circuit is that the control potential applied to the cathode atects the voltage between the anode and cathode of tube 2 and therefore atects the tubes characteristics, including the cut-oit point. If the cut-oi point does not vary linearly With anode voltage, as will be found to be more or less the case in commercial tubes, the linearity between conytrol potential and delay is destroyed. This diculty is overcome in accordance with the invention by dividing the anode load resistance into two parts 16 and 17 and connecting a gas-filled voltage regulator tube 15, which may be a simple neon lamp, from point A between the two resistors to the cathode. With this arrangement the potential of point A relative to the cathode is Asubstantially xed and independent of the Value of the control potential, or range voltage, applied to the cathode. Variations in control potential therefore cannot influence the`anode-cathode potential of the tube during cut-otl and anode conduction will occur at the same grid-cathode potential for all values of the control potential.

What I claim is:

1. A delayed pulse generator comprising a vacuum tube having an anode, a cathode and a control grid, a source of voltage varying as a function of time, a source `of adjustable direct voltage, means for applying the algebraic Isum of said voltages between the grid and cathode of said tube, a circuit connected between the anode and cathode of said tube and containing in series an anode load resistor, a source of positive potential and said source of adjustable direct voltage, and means connected between an intermediate point on said load resistor and the cathode for maintaining said point at a fixed positive potential relative to said cathode.

2. A delayed pulse generator comprising a vacuum tube having an anode, a cathode and a control grid, a source of direct voltage varying as a function of time connected between said gridand a point of reference potential, a source of adjustable direct voltage connected between said cathode and said point of reference potential, an anode load resistor and a source of positive potential connected in a series between said anode and said point of reference potential, and means connected -between an intermediate point on said anode load resistor and said cathode for maintaining said point at a fixed positive potential relative to said cathode.

3. Apparatus as claimed in claim 2 in which said means is a gaseous discharge tube.

4. In an automatic radar range tracking circuit of the type employing a range gate, means for delaying the range gate relative tothe transmitted radar pulse, and means responsive to said range gate and the target signal for generating a range voltage and for applying said range voltage to said delay means for controlling the delay of said range gate, and in which said delay means comprises a delay triode having a voltage synchronized with said transmitted pulse and varying linearly with time applied between its grid and apoint of reference potential and having said range voltage applied between its cathode and said point of reference potential and further having an anode load resistor connected between its anode and said point of referencepotential, means for removing the influence of said range voltage on the value of gridcathode voltage at which said triode passes from a nonconductive to a conductive state, said means comprising a constant potential gaseous discharge device connected between an intermediate point on said anode resistor `and the cathode of said triode.

t References Cited in the file of this patent UNITED STATES PATENTS 2,420,374 Houghton May 13, 1947 2,578,256 'MacNichol Dec. 1l, 1951 2,689,952 Johnson et al. Sept. 2l, 1954 

